Same squares, same sharpness.

Texel density is how many pixels of texture cover one metre of surface. See it with a checker map, compute it in px/m, match it with S, Average Islands Scale, Pack Islands and Set TD as in Blender, choose a target from the camera and the memory, and learn when to break the rule.

STAGE
    UV Editor
    Image
    LMB select · Shift add · G S R · Wheel zoom · MMB pan
    3D Viewport
    Shading
    LMB select · MMB orbit · Wheel zoom
    LMBSelectGMoveSScaleRRotateAAllCtrlAAverageHomeFrameCtrlZUndo
    KEY IDEAS

    Pixels per metre

    Three things decide the density together. Change any of them and the checker squares change size.

    Texel density
    The texture pixels that a 1 m ruler on the surface covers (px/m). It is measured on the model: texture size, UV size and object size. The camera does not change it.
    The formula
    Texture size × √(UV area ÷ 3D area). For a square island: island px ÷ face m.
    Checker map
    Every square is the same number of texels: same square size = same density.
    Target
    The density you aim for, chosen per project from how close the camera gets (how big things look on screen) and the memory: about 512 px/m for third person, 1024 px/m for first person.
    Texture size
    ≈ target × size of the object in metres, rounded up to a power of two.
    Memory
    2 × the density = 4 × the pixels. A 2K texture costs four times a 1K.